Commitments and Contingencies Commitments and Contingencies - Narrative (Details)					3 Months Ended				12 Months Ended
		Nov. 04, 2016	Nov. 01, 2015 USD ($)	Sep. 23, 2015 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) MW	Dec. 31, 2017 USD ($) MW	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2017	Dec. 31, 2017 claimant	Dec. 31, 2017 MGPSite	Dec. 31, 2017 employee	Jun. 30, 2016 USD ($)	Feb. 17, 2012 USD ($)
Commitments and Contingencies [Line Items]
Document Period End Date									Dec. 31, 2017
Direct Investment Commitment																		$ 1,000,000,000
Power Volume | MW								10	220
BusinessAcquisitionResidualcommitment | MW								55
Loss Contingency, Loss in Period										$ 50,000,000
Nontrade Receivables, Current	[1]				$ 94,000,000			$ 109,000,000	$ 94,000,000	109,000,000
Nontrade Receivables, Noncurrent	[2]				15,000,000			15,000,000	15,000,000	15,000,000
Accounts Payable, Other, Current	[1],[3]				(11,000,000)			(13,000,000)	(11,000,000)	(13,000,000)
DOE Spent Nuclear Fuel One Time Fee					34,000,000				34,000,000
Operating Expenses	[4]								29,720,000,000	28,200,000,000	$ 25,056,000,000
Loss Contingency, Damages Awarded, Value												$ 14,000,000
Maximum [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					10,000,000				10,000,000
Exelon Generation Co L L C [Member]
Commitments and Contingencies [Line Items]
Entity Number of Employees | employee																1,500
Leasehold Improvements, Gross								110,000,000		110,000,000
Lessee, Operating Lease, Term of Contract		20 years
Costs Incurred, Development Costs									457,000,000
Nuclear financial protection pool value					450,000,000				450,000,000
Maximum recovery limit from a nuclear industry mutual insurance company in the event of multiple losses					13,000,000,000				13,000,000,000
Maximum annual assessment payment mandated by Price-Anderson Act for a nuclear incident					2,800,000,000				2,800,000,000
Mutual Insurance Total Retrospective Premium Obligation					360,000,000				360,000,000
Mutual Replacement Power Cost Insurance Maximum Retrospective Premium Obligation					3,200,000,000				3,200,000,000
Cost of spent nuclear fuel disposal per kWh of net nuclear generation					0.001				0.001
Spent Nuclear Fuel Storage Reimbursement	[5]								1,167,000,000
Spent Nuclear Fuel Storage Reimbursement Net Co Owners	[5],[6]								1,006,000,000
DOE Spent Nuclear Fuel One Time Fee					277,000,000				277,000,000
DOE Spent Nuclear Fuel One Time Fee With Interest					1,147,000,000			1,024,000,000	$ 1,147,000,000	1,024,000,000
Spent Nuclear Fuel Treasury Interest Rate									1.149%
Total cost of remediation to be shared by PRPs									$ 90,000,000
Loss Contingency Accrual, Provision					20,000,000
Environmental loss contingencies								90,000,000		90,000,000
Asbestos Liability Reserve					78,000,000			83,000,000	78,000,000	83,000,000
Asbestos Liability Reserve related to open claims					21,000,000				21,000,000
Open Asbestos Liability Claims | claimant														230
Asbestos liability reserve related to anticipated claims							$ 57,000,000
Exelon Generation Co L L C [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Direct Investment Commitment					450,000,000				$ 450,000,000
Business Acquisition, Expected New Generation Mwh | MW									285
Exelon Generation Co L L C [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Direct Investment Commitment					500,000,000				$ 500,000,000
Business Acquisition, Expected New Generation Mwh | MW									300
Exelon Generation Co L L C [Member] | West Lake [Member]
Commitments and Contingencies [Line Items]
Loss Contingency Accrual, Provision					340,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Nuclear insurance liability limit per incident					13,400,000,000				$ 13,400,000,000
Exelon Generation Co L L C [Member] | Nuclear Insurance Premiums [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Nuclear financial protection pool value						$ 420,000,000
Exelon Generation Co L L C [Member] | Guarantees Other Than Letters Of Credit and Nuclear Insurance Premiums [Member]
Commitments and Contingencies [Line Items]
Mutual Property Insurance Distribution To Members					60,000,000			21,000,000	60,000,000	21,000,000	$ 21,000,000
Exelon Generation Co L L C [Member] | Unasserted Claim [Member]
Commitments and Contingencies [Line Items]
Accrued Liabilities and Other Liabilities																	$ 14,000,000
Commonwealth Edison Co [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															42
Sites approved for clean-up | MGPSite															19
Sites under study/remediation | MGPSite															23
Other Increase (Decrease) in Environmental Liabilities						13,000,000
PECO Energy Co [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															26
Sites approved for clean-up | MGPSite															17
Sites under study/remediation | MGPSite															9
Other Increase (Decrease) in Environmental Liabilities						$ 2,000,000
Baltimore Gas and Electric Company [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															13
Sites approved for clean-up | MGPSite															11
Sites under study/remediation													13,000,000		2
Common Equity Tier One Capital Ratio													48.00%
Occupancy, Net			$ 42,000,000	$ 12,000,000
Operating Leases, Income Statement, Initial Direct Costs								25,000,000
Oil and Gas Property, Lease Operating Expense								29,000,000
Operating Expenses								28,000,000
Pepco Holdings LLC [Member]
Commitments and Contingencies [Line Items]
Number of Real Estate Properties | MGPSite															9
Environmental Remediation Expense							$ 10,000,000
Pepco Holdings LLC [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					7,000,000				7,000,000
Pepco Holdings LLC [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss					18,000,000				18,000,000
Potomac Electric Power Company [Member]
Commitments and Contingencies [Line Items]
Common Equity Tier One Capital Ratio													48.00%
Accrued Liabilities and Other Liabilities					$ 28,000,000			$ 0	$ 28,000,000	$ 0
Delmarva Power and Light Company [Member]
Commitments and Contingencies [Line Items]
Total number of MGP sites | MGPSite															3
Sites approved for clean-up | MGPSite															2
Common Equity Tier One Capital Ratio													48.00%
Atlantic City Electric Company [Member]
Commitments and Contingencies [Line Items]
Common Equity Tier One Capital Ratio													48.00%

[1] Recorded in Accounts receivable, other.

[2] Recorded in Deferred debits and other assets, other

[3] Non-CENG amounts owed to co-owners are recorded in Accounts receivable, other. CENG amounts owed to co-owners are recorded in Accounts payable. Represents amounts owed to the co-owners of Peach Bottom, Quad Cities, and Nine Mile Point Unit 2 generating facilities.

[4] Includes gross utility tax receipts from customers. The offsetting remittance of utility taxes to the governing bodies is recorded in expenses on the Registrants’ Consolidated Statements of Operations and Comprehensive Income. See Note 24 — Supplemental Financial Information for total utility taxes for the years ended December 31, 2017, 2016 and 2015.

[5] Includes $53 and $49, respectively, for amounts received since April 1, 2014, for costs incurred under the CENG DOE Settlement Agreements prior to the consolidation of CENG.

[6] Total after considering amounts due to co-owners of certain nuclear stations and to the former owner of Oyster Creek.